Abstract

Energy harvesting from human body motion has been investigated extensively in the last two decades due to the increasing demand for Smart Wearables. Smart Wearables are beneficial in terms of daily monitoring of vital parameters and early recognition of diseases. However, continuous and close-meshed monitoring in daily life is often facing the obstacle of limited energy storage. Integrated sensors and electronics of Smart Wearables may be powered in a conventional manner by energy storage. But energy storage such as battery is subject to restrictions as limited lifetime and charging process. Thus, the development of self-powering Smart Wearables is highly promising. The conversion of human body motion into electrical energy is significant for the identification of medical application areas.

Investigations on energy harvesting from human body motion is facing limitations such as low frequency range of body motion, low accelerations as well as wearing comfort. Numerous studies address the use of piezoelectric ceramics for energy harvesting. However, the high mass density and the high modulus of elasticity limit energy harvester designs based on piezoelectric ceramics to rather heavy wearables. In terms of lightweight designs, polymers such as PVDF (polyvinylidene fluoride) have been considered as functional materials in several researches but these materials are disadvantageous regarding energy efficiency. Auspicious functional materials for energy harvesting from body motion are piezoelectric electrets (piezoelectrets, also referred to as ferroelectrets) due to their high piezoelectric coefficients and low mass density. Piezoelectrets facilitate the implementation of lightweight energy harvester designs with high output power that is advantageous for applications in context of Smart Wearables. In particular, fluorethylpolypropylene (FEP) piezoelectrets with parallel-tunnel structures are promising generators for energy harvesting. Within the present work, a novel design of parallel-tunnel FEP energy harvester in 31-mode is introduced and validated by means of an experimental setup.

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